Detecting previously unexplored cosmic phenomena with an instrument small enough to fit on a table. This is the innovative mission of TANGO – Transducer Antenna for a Noiseless Gravitational Observatory, a project that aims to develop a new generation of gravitational-wave detectors measuring just a few tens of centimetres and capable of operating at temperatures close to absolute zero. Led by Matteo Borghesi, a researcher at the University of Milano-Bicocca, the project has been awarded an ERC Starting Grant of €1,499,312 by the European Union, which will also make it possible to establish a dedicated research team.
Gravitational waves are tiny ripples in space-time generated by the most energetic events in the Universe, such as the merger of black holes or neutron stars. When they reach Earth, after travelling for millions or even billions of years, they produce incredibly small distortions. Their first observation in 2015 confirmed one of the most important predictions of Einstein’s general theory of relativity and inaugurated a new form of astronomy, capable of observing phenomena invisible to traditional telescopes. Since then, hundreds of signals from known astrophysical sources have been detected, but a large part of the gravitational-wave spectrum remains unexplored.
TANGO was created precisely to explore this still unknown region, between 100 kHz and 10 MHz: the so-called high-frequency gravitational-wave band. Signals associated with dark matter, primordial black holes or other phenomena that escape current theories could emerge within this range.
«This band,» observes Matteo Borghesi, researcher at the Department of Physics, «is particularly interesting because it is relatively quiet: very few known sources are in fact capable of producing gravitational waves at these frequencies and, despite growing experimental efforts, no signal has yet been observed. The unequivocal observation of a signal in this region would represent a major discovery, with the potential to transform our understanding of the Universe.»
The project brings together two frontiers of research: the study of gravitational waves, which investigates the most extreme phenomena in the cosmos, and quantum technologies, developed to control and measure matter at the smallest scales. By combining these two fields, TANGO aims to create a new generation of extremely compact gravitational-wave detectors, measuring just a few tens of centimetres and operating at temperatures close to absolute zero (-273°C), where noise caused by the thermal motion of matter is drastically reduced.
«At the heart of the detector,» explains Matteo Borghesi, project coordinator, «are two coupled oscillators: a small quartz crystal and a superconducting electromagnetic cavity. Thanks to techniques developed in the field of quantum technologies, the electromagnetic system can be used to control the state of the crystal, removing energy from its vibrations and bringing it to effective temperatures more than one hundred times lower than those achievable with standard cryogenic systems. Under these conditions, the crystal becomes extraordinarily quiet, making it possible to distinguish extremely weak signals, such as those produced by the passage of a gravitational wave.»
The University of Milano-Bicocca is consolidating the work carried out in recent years by two of its facilities dedicated to frontier research: BiCoQ, the Centre for Quantitative Cosmology, and BiQuTe, the Interdepartmental Centre for Quantum Technologies. In particular, the TANGO project has its roots in the BAUSCIA – Bulk Acoustic Wave Sensors for High-frequency Antennas research line of the Department of Physics, a Department of Excellence.
«TANGO,» says Leo Ferraris, Pro-Rector for Research, «represents the natural evolution of the experience developed in the field by our University and aims to build an instrument capable of exploring a region of the Universe that has so far remained inaccessible. The important recognition awarded to Matteo Borghesi confirms the innovative nature of his proposal and, more broadly, the competitiveness of Milano-Bicocca’s research in an international context.»
Since 2014, the University of Milano-Bicocca has received funding for 22 ERC projects: 7 Starting Grants, including TANGO, 9 Consolidator Grants, 2 Advanced Grants, 2 Proof of Concept grants and 2 Synergy Grants.